In the field of semiconductor manufacturing, lithography has been the main stream approach to pattern semiconductor devices. In typical prior art lithography process, a UV light is projected onto a silicon wafer coated with a thin layer of photosensitive resist through a mask that defines a particular circuitry pattern. Exposure to UV light, followed by subsequent baking, induces a photochemical reaction which changes the solubility of the exposed regions of the photosensitive resist. Thereafter, an appropriate developer, usually an aqueous base solution, is used to selectively remove the resist either in the exposed regions (positive-tone resists) or, in the unexposed region (negative-tone resists). The pattern thus defined is then imprinted on the silicon wafer by etching away the regions that are not protected by the resist with a dry or wet etch process.
Many of the currently available resists are chemically amplified resists which are made of two major components: The first component of such chemically amplified resists is an aqueous base soluble polymer which contains polar functional groups and acid labile protecting groups. The protected sites of the aqueous base soluble polymer convert the polymer into an aqueous insoluble polymer. The second major component of prior art chemically amplified resists is a photoacid generator. Exposure of these resists to UV irradiation typically generates a catalytic species as a result of the photochemistry of the acid precursor. The catalytic species is believed to induce a cascade of subsequent chemical transformations of the resist that alter the solubility of the exposed regions. Thus, the quantum efficiency of the photochemical event is amplified hundreds or even thousands of times through the catalytic chain reaction. The most commonly employed chemical amplification involves the acid catalyzed deprotection of various partially protected poly(p-hydroxystyrene) or poly(acrylic acid) for positive-tone resists. See, for example, U.S. Pat. Nos. 4,491,628 and 5,585,220.
In e-beam lithography applications, the chemically amplified resist is typically coated on a wafer and/or a quartz plate well in advance of mask formation. In the time between formation of the coating and pattenwise e-beam exposure of the resist coating in an e-beam exposure tool, the resist may undergo changes which effect its performance in the e-beam tool in an unpredictable manner. To avoid this shelf-life problem, the coated wafers or quartz plates are stored under vacuum or an inert gas to prevent contamination by water and/or air.
In addition to exhibiting shelf-life problems on storage of the resist-coated plate or wafer, the prior art resists may undergo alterations in the e-beam tool itself during the lithographic process. In e-beam processes, the lithographic pattern is formed by sequentially exposing small areas of the coated wafer or plate. The entire e-beam exposure process is typically carried out under high vacuum. Thus, the area of resist last exposed will spend a significantly less amount of time in high vacuum after being exposed to the e-beam relative to the areas of resist exposed at the beginning of the lithographic process. Problems arise where the properties of the resist in the last exposed areas are different from in the first exposed areas because of the difference in length of time in the vacuum.
In view of the above problems associated with prior art chemically amplified resists, it would be highly beneficial to provide a new and improved resist and resist system which do not exhibit any significant shelf-life or vacuum effect problems. Such a new resist and resist system would be especially beneficial in the field of e-beam lithography wherein such problems are generally found.